Gate valves are provided in a vacuum apparatus or the like, and the gate valves separate two spaces in which the vacuum degrees thereof are different from each other such as between a chamber and pipes, between pipes, between a pipe and a pump, or the like; and the gate valves communicate the two spaces. As such a gate valve, various valves are known.
For example, a structure is known in which a valve plate is inserted into a valve opening-closing position of a flow passage by sliding a valve plate, furthermore, the flow passage is separated (valve closing operation) or flow passages are communicated by operating the aforementioned valve plate (valve opening operation) by operating this valve plate. Additionally, the valve plate is moved to a safety position located in a valve box from the flow passage by sliding the valve plate. As a valve having such a structure, a pendulum valve, a direct acting valve, a door valve, or the like is known.
A direct acting gate valve has a constitution in which a valve plate is disposed in a hollow portion of a valve box. A first opening portion and a second opening portion constituting a flow passage are formed at the valve box. The valve plate is securely fixed to a valve rod (support body). In this structure, the aforementioned valve plate is inserted into the valve opening-closing position of the opening portion (flow passage) by moving straight the aforementioned valve rod in the longitudinal direction thereof, or the aforementioned valve plate is moved to the safety position at which the opening portion is not formed.
As a conventional direct acting gate valve, a gate valve is known which is provided with a valve body that is configured to include two of a first valve plate and a second valve plate which are connected to each other with bellows interposed therebetween, an actuator be disposed at the center portion of the valve plate between these two valve plates, and a valve box at which an opening portion constituting the flow passage is formed. In this gate valve, the flow passage is closed due to the first valve plate coming in contact with and pressing onto the peripheral inner surface of the opening portion of the valve box by operating the actuator, or the flow passage is released due to separating the first valve plate from the inner surface of the aforementioned valve box by operating the actuator (for example, refer to Patent Document 1).
Additionally, a pendulum gate valve has a constitution in which a valve box having a hollow portion, a support body, and a valve body (a valve plate in the case of the structure in which a seal ring plate is provided at an opening portion) which is securely fixed to this support body. In the valve box, a first opening portion and a second opening portion constituting a flow passage are formed. The support body is securely fixed to a rotation shaft in the hollow portion and is expanded in a direction parallel to the plane perpendicular to the rotation shaft. In this gate valve, the aforementioned valve body is turned by rotating the aforementioned rotation shaft, therefore, the above-described valve body is inserted into the valve opening-closing position of the opening portion (flow passage) or the above-described valve body is moved to the safety position at which the opening portion is not formed.
As a conventional pendulum gate valve, a constitution is known in which a valve plate that is capable of rotating around a rotation shaft in a hollow portion of a housing, a slidable seal ring plate that is disposed at an opening portion of the housing, and an actuator allowing the aforementioned seal ring plate to slide on a flange formed integrally with the housing are provided. In this gate valve, the flow passage is closed due to the aforementioned seal ring plate coming in contact with and pressing onto the aforementioned valve plate, or the flow passage is released by separating the aforementioned seal ring plate from the aforementioned valve plate (for example, refer to Patent Document 2).
The actuator provided in this pendulum gate valve has a structure in which a bolt, a ring-shaped chamber (cylinder), a piston, and a spring are arranged in series in the sliding direction of the seal ring plate. For this reason, when the flow passage is being closed, the restorative force generated in the spring is transmitted to the seal ring plate through the piston, the cylinder, and the bolt.
As such a pendulum gate valve, a valve is disclosed which airtightly blocks a flow passage, has degree of abrasion resistance, and is ease in maintenance (for example, refer to Patent Document 3). In this gate valve, an outer valve body is connected to a drive unit via an arm, and the outer valve body vertically moves in an opening axis. Consequently, an activation device which prompts the arm to vertically move via a power transmission device needs a considerable driving power depending on an increase in a surface area of the gate valve.
Additionally, in the case of applying the configuration disclosed in Patent Document 3 to a large-scale gate valve, in addition to that the volume of an O-ring that is to be pressed increases, the O-ring is disposed at a position distant from the rotation shaft. Because of this, since it is required to design the rotation shaft so as to become a rigid body that bears against a necessary moment load, it contributes to an increase in a weight of the gate valve.
Accordingly, although the configuration disclosed in Patent Document 3 is effective to a small gate valve, it is unsuitable for a large-scale gate valve.
The inventors have developed a gate valve having a configuration which can increase a surface area of the aforementioned gate valve and can carry out isolation operation with a high degree of reliability by a simple configuration, and filed a patent application (Patent Document 4). In this gate valve, a movable valve that forms a valve body is configured to include a plurality of movable valves in a stacking direction (for example, a movable valve frame (first movable valve), a movable valve plate (second movable valve)), and an air cylinder (second force-applying unit) is provided at a position at which both movable valves are connected. In order to drive the air cylinder, it has been necessary to provide, inside the movable valve frame (first movable valve), a line (supply line) that extends from the outside of the gate valve to the air cylinder through the rotation shaft of the gate valve and introduces compressed air thereinto.
In the valve body structure in which the air cylinder or the supply line are provided inside the gate valve as stated above, although isolation operation with a high degree of reliability can be realized, a weight of the valve body increases, a large driving power is necessary when the valve body moves upward and downward or the valve body moves while revolving, and therefore simplification of the configuration of the valve body and weight saving thereof have been required.
Moreover, in the mechanism including an air cylinder inside the valve body, in the case where the proportion of the surface area receiving a pressure to the valve body is, for example, 25%, the cancellation rate of a back pressure is approximately 75%, a large sealing force tends to be required. Consequently, development of an excellent back pressure cancellation mechanism has been expected. Here, the back pressure means that a pressure is applied to a valve body in a direction from a valve closed state to a valve opened state, and a back pressure cancellation mechanism means a mechanism that does not directly oppose the back pressure (a mechanism that does not generates a back pressure).